1. Field of the Invention
Described herein are devices relating to lighting fixtures, such as suspended linear lighting fixtures, that are well suited for use with solid state lighting sources, such as light emitting diodes (LEDs).
2. Description of the Related Art
Lighting fixtures, such as Troffer-style lighting fixtures, are ubiquitous in commercial office and industrial spaces throughout the world, oftentimes being designed to have a spatially convenient and aesthetically pleasing linear appearance. To this end, many of these lighting fixtures house linear elongated fluorescent light bulbs that span the length of the troffer. These lighting fixtures can be mounted to or suspended from ceilings, and can be at least partially recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. U.S. Pat. No. 5,823,663 to Bell, et al. and U.S. Pat. No. 6,210,025 to Schmidt, et al. are examples of typical troffer-style fixtures.
More recently, with the advent of the efficient solid state lighting sources, troffers and other commercial lighting fixtures have been developed that utilize LEDs as their light source. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED.
LEDs have certain characteristics that make them desirable for many lighting applications, such as troffers, that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in their LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications, including commercial lighting fixtures. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving.
LEDs can be arranged in different ways in the above mentioned lighting fixtures, with some fixtures having LEDs incorporated into a linear lighting device and having a structure similar to a florescent tube. These “tube” LED devices can resemble a linear florescent bulb and have electrodes and pins at both ends of their linear structure. Furthermore, suspended fixtures incorporating such linear lighting devices typically hold the lighting devices in place with mechanical support at both ends of their linear structure.
While such lighting fixtures are presently used, these fixtures are limited in how they can be designed and spatially arranged. For example, in the above described linear lighting fixtures, electrical and mechanical connections at both ends of an incorporated lighting device (i.e. a florescent tube, linear LED device, etc.) are typically required. This requirement inhibits freedom of design and arrangement of such fixtures and oftentimes requires the use of bulky additional components such as large troffer bodies. These additional components take up space, provide additional features that are subject to device failure and generally increase the time and cost of manufacturing such devices. Furthermore, these fixtures are usually fixated in a certain structure or arrangement and are not freely adjustable.